1. Field of the Invention
The present invention relates generally to a rewritable optical recording medium system, and more particularly to an apparatus and method for discriminating between a land track and a groove track in a land/groove recording system having the structure where a signal track is composed of the land and the groove.
2. Background of the Related Art
With the growth of audio and video media, an optical recording/reproducing apparatus for recording and reproducing audio/video data on a semipermanent optical recording medium have been developed.
In case of the optical recording medium, as the storage capacity of the existing CD-ROM title reaches the uppermost limit, a digital versatile disc (DVD) is in the spotlight as a new optical recording medium. The DVD recognizes data in the same manner as a compact disc (CD) which recognizes data of “0” and “1” according to reflecting angles of a laser. However, the storage width of data in the DVD is minute in comparison to that in the CD.
Like the CD, the DVD is been developed from the technique of reproducing the data recorded on the disc to the technique of freely and repeatedly recording the data on the disc. In order to achieve this, various kinds of rewritable DVDs have been proposed lately. One among them, there exists a DVD where a disc track is divided into a land and groove (hereinafter referred to as ‘land/groove’ or ‘L/G’) tracks, and the data is recorded in the respective tracks (for instance, DVD-RAM).
FIG. 1 is a block diagram illustrating the construction of a typical apparatus for recording and reproducing data on the optical recording medium. Referring to FIG. 1, under the control of a servo control section 106, an optical pickup 102 places an optical beam condensed through an object lens on a signal track of an optical recording medium, i.e., an optical disc 101, and makes the optical beam reflected from a signal recording surface of the track condensed through the object lens and incident to an optical detector to detect a focus error signal and a tracking error signal. The optical detector is composed of several optical detecting elements, which output to a radio frequency (RF) and servo error generating section 104 electric signals in proportion to quantities of light obtained by the respective optical detecting elements.
For example, if the optical detector is composed of four optical detecting elements PDA, PDB, PDC, and PDD divided by four in a signal track direction and in a radial direction, the optical detector outputs to the RF and servo error generating section 104 electric signals a, b, c, and d in proportion to quantities of light obtained by the respective optical detecting elements PDA, PDB, PDC, and PDD (see FIG. 2).
The RF and servo error generating section 104 generates an RF signal required for data reproduction, read channel 2 signal required for servo control, focus error signal, etc., by combining the electric signals a, b, c, and d.
Here, the RF signal (also called ‘read channel 1 signal’) may be obtained by computing (a+b+c+d) of the electric signals outputted from the optical detector, and the read channel 2 signal by computing (a+d)−(b+c). The tracking error (TE) signal may be obtained by processing the read channel 2 signal.
Meanwhile, if the optical detector is divided by two in a track direction, i.e., into two photodiodes I1 and I2, the RF signal (=I1+I2) and read channel 2 signal (=I1−I2) are detected from the balance of the light quantities of the photodiodes. In other words, a+d and b+c in FIG. 2 correspond to I1 and I2, respectively.
At this time, the RF signal is outputted to a data decoder 105 for data reproduction, the servo error signal such as FE and TE to a servo control section 106, and the control signal for data recording to an encoder 103.
The encoder 103 encodes the data to be recorded to recording pulses of a format required by the optical disc 101, and records the pulses on the optical disc 101 through the optical pickup 102. The decoder 105 restores the data of the original form from the RF signal.
Meanwhile, a host such as a personal computer (PC) may be connected to the optical disc recording/reproducing apparatus. This host transmits a recording/reproducing command to a microcomputer 111 through an interface 110, transmits the data to be recorded to the encoder 103, and receives reproduced data from the decoder 105. The microcomputer 111 controls the encoder 103, decoder 105, and servo control section 106 in accordance with the recording/reproducing command from the host.
At this time, an advanced technology attached packet interface (ATAPI) is typically used as the interface 110. Specifically, the ATAPI is the interface standard between the host and the optical recording/reproducing apparatus such as a CD or DVD driver proposed to transmit the data decoded by the optical recording/reproducing apparatus to the host, and serves to convert the decoded data into a protocol of a data packet that can be processed in the host and transmit the data packet.
Meanwhile, the servo control section 106 processes the focus error signal (FE), and outputs a driving signal for focusing control to a focus servo driving section 107. The servo control section 106 also processes the tracking error signal (TE), and output a driving signal for tracking control to a tracking servo driving section 108.
The focus servo driving section 107 moves the optical pickup 102 up and down by driving a focus actuator in the optical pickup 102, so that the optical pickup 107 follows the movement of the rotating optical disc 101.
The tracking servo driving section 108 moves the object lens of the optical pickup 102 in a radial direction by driving a tracking actuator in the optical pickup 102, so that the object lens corrects the position of the optical beam, and follows the track.
If the DVD is a rewritable disc, for example, DVD-RAM, where the signal track is composed of the land and groove, the data can be recorded on or reproduced from both the land track and the groove track as well as either of the land track and the groove track. Here, the land track and the groove track have different depths in a light incident direction. For instance, the DVD-RAM has a depth difference of λ/6 between the land track and the groove track.
FIG. 3 illustrates an example of a disc having the above-described L/G track structure. Referring to FIG. 3, the track protruded in the incident direction of the optical beam from the optical pickup 102 is defined as a groove track 2, and the track arranged to alternate with the groove track and depressed from the incident optical beam is defined as a land track 3. Accordingly, there is a predetermined height difference d between the groove track 2 and the land track 3. The track pitch (TP) is different according to the kind of disc, but is commonly 1 μm or less.
As shown in FIG. 4, each track is composed of a plurality of sectors which are a data region, and a header region which includes sector position information and control information and which is positioned between the respective sectors. The header region is pre-formatted, and thus the tracking control can be effected in a blank disc where no information signal is recorded.
The header region is a region where data cannot be recorded, is used for obtaining various kinds of information for performing the recording and reproduction, and is generally predetermined by a disc manufacturer.
The header region is briefly classified into two kinds. As shown in FIG. 4, one is a header region 8 positioned between sectors in the same track (hereinafter referred to as ‘header region within a track’), and the other is a header region 9 positioned between the last sector 4 of the land track and the first sector 5 of the groove track (hereinafter referred to as ‘header region between tracks’). Accordingly, the optical disc recording/reproducing apparatus as shown in FIG. 1 can discriminate the track kind at the present position from the header region within a track, and recognize the track changeover from the header region between tracks, so that the servo suitable for the changed track can be performed.
FIG. 5 illustrates in detail ‘A’ and ‘B’ portions in FIG. 4. Referring to FIG. 5, the header region has a first header field 91 phase-converted centering around a track center, and a second header field 92. If the disc is the DVD-RAM, the first and second header fields include two header fields, respectively.
In the header region where the land track switches over to the groove track, the first header field is first detected at a position higher than the track center, and then the second header field is detected at a position lower than the track center. On the contrary, in the header region where the groove track switches over to the land track, the first header field is first detected at a position lower than the track center, and then the second header field is detected at a position higher than the track center.
Meanwhile, the control information recorded in the header region may be recorded in a wobbling form along the track. Here, the wobbling means that the control information is recorded on a boundary surface of the track by the change of a laser beam of a laser diode by supplying to the power of the laser diode information to be applied to the disc by modulating a predetermined clock signal, for example, information on the corresponding position, information on the rotating speed of the disc, etc.
Referring to FIG. 6, it can be recognized that the track boundary surface of the sector which is the data region arranged between the header regions has the wobbling form. Specifically, (a) in FIG. 6 shows an example of a wobbling signal in the groove track, and (b) shows an example of a wobbling signal in the land track. Here, no wobbling signal is recorded in the header region.
In order to perform the recording/reproduction on the optical disc having the structure where the signal track is composed of the land and the groove, the optical beam should accurately follow the center of the land and groove tracks. At this time, the optical beam should be controlled in a different manner according to the land and groove tracks, and thus it is important to accurately discriminate the kind of the track.
As shown in FIG. 3, since the respective tracks have the height difference and the track pitch is very dense, there exists a difference in DC offset (produced in signal due to the L/G depth difference) when the focusing or tracking servo is performed. Also, the tracking error signal in the land has an opposite phase to the tracking error signal in the groove. However, in order to normally follow both the land and groove tracks, the tracking error signals obtained from the land and the groove have the same phase.
Accordingly, the kind of the track to be recorded/reproduced should be discriminated in advance, and the servo should be performed accordingly. Specifically, in the land track, the tracking servo should be performed by the tracking error signal offset-adjusted and inverted to match the land, while in the groove track, the tracking servo should be performed by the tracking error signal offset-adjusted and inverted to match the groove. In order to achieve this, it should be rapidly and accurately discriminated whether the track where the optical beam is currently positioned is the land or the groove.
A conventional method of discriminating whether the track is the land or the groove uses the header region as shown in FIG. 7. The phase of the tracking error signal in the header region in case of following the land track is opposite to the phase of the tracking error signal in case of following the groove track.
Referring to FIG. 7, the read channel 2 signal generated from the RF and servo error generating section 104 or the tracking error signal obtained by processing the read channel 2 signal is inputted to first and second comparators 201 and 202. At this time, since the first header field and the second header field in the header region are alternately arranged on the basis of the track center, the read channel 2 signals detected from the first header field and the second header field have the phases (i.e., tilts) opposite to each other.
For the convenience in explanation, it is assumed that the header signal detected at a position higher than the track center is a first header region signal IP1, and the header signal detected at a position lower than the track center is a second header region signal IP2.
If the read channel 2 signal inputted to a plus terminal of the first comparator 201 is higher than a slice level signal inputted to a minus terminal thereof, the first comparator 201 outputs to an L/G discriminating section 203 the first header region signal IP1 as shown as (a) in FIGS. 8 and 9. If the read channel 2 signal inputted to a minus terminal of the second comparator 202 is lower than the slice level signal inputted to a plus terminal thereof, the second comparator 202 outputs to the L/G discriminating section 203 the second header region signal IP2 as shown as (b) in FIGS. 8 and 9.
At this time, the phases of the IP1 signal and the IP2 signal are changed according to the fact that the currently following track is the land or the groove as shown in FIGS. 8 and 9. The header region where the land track switches over to the groove track is detected as shown in FIG. 8, and the header region where the groove track switches over to the land track is detected as shown in FIG. 9.
Accordingly, the L/G discriminating section 203 discriminates the track by the detection order of the IP1 and IP2 signals, and outputs a track switchover signal L/G SW as shown as □ in FIGS. 8 and 9 to the servo control section 106, so that the servo control section 106 performs the servo control suitable to the changed track.
However, though the conventional track discriminating method as described above can be used without any problem in case that the IP1 and IP2 signals are accurately detected in the header region by the stable performance of the servo, there is a possibility that a signal having a similar waveform to the above signals is detected anywhere of the disc, and such a possibility becomes greater in case that the system is unstable.
Here, the time point where the servo is unstable may be the case that the system is initially operated, or a track jump or track cross is performed. In this case, the IP1 and IP2 signals are detected unstably, and it is unreliable that the IP1 and IP2 signals are the signals detected from the header region as well. If the IP1 and IP2 signals are not accurately detected as above, the land/groove track discrimination also becomes inaccurate. Accordingly, the tracking and focusing servo cannot be performed properly, and this causes much time to be required for reaching the normal recording/reproduction, and the recording/reproduction itself to be impossible in the worst case.